(1) Field of the Invention
The present invention relates to plethysmographs used for measuring changes in air volume, such as in non-invasive pulmonary testing of small animals, and in particular to plethysmographs that include an animal restraint to facilitate attachment of a barrier seal and insertion of the test animal into the plethysmograph chamber.
(2) Description of the Prior Art
Plethysmographs are used in research to collect data relating to changes in air pressure within a test chamber. An example of such data is pulmonary data from small animals, such as mice. Most plethysmographs are comprised of a test chamber to enclose the test subject, and a transducer port connected via tubing to a differential pressure transducer. As changes to the air volume within the test chamber occur, pressure variations are recorded by the transducer, which normally displays the recorded data in numerical form or as a graph.
Plethysmographs are commonly used to measure the pulmonary activities of mice and other small animals that are completely or substantially enclosed within the test chamber. As the test animal inhales or exhales, the changes in air volume results in pressure variations that are recorded by the transducer, which normally displays the recorded data in numerical form or as a graph.
The plethysmograph may also include a reference chamber to partially reduce the affect of background noise resulting from variations in air pressure entering the test chamber, with the reference chamber having a port connected to the transducer. The transducer simultaneously measures variations in air pressures within the test and reference chambers, and subtracts the reference chamber measurements from the test chamber measurements. As a result, the net pressure variations are essentially attributable to the respiration patterns of the test animal. Preferably, the test and reference chamber pneumotachs through which the air enters the chambers are close to each other to minimize variations in exterior air patterns.
In one type of plethysmograph, known as a dual-chamber plethysmograph, two chambers, the nasal and thoracic chambers, are attached end-to-end at their respective attachment openings, with a barrier seal being fitted between the chambers to prevent passage of air between the chambers. The seal, sometimes referred to as a neck seal or nose seal, includes a central opening sized to receive at least part of the test animal's head including the nose, i.e., only the animal's nose up to all of the animal's head may be inserted through the seal opening. As used herein, a statement to the effect that the “head” of the test animal is inserted through the seal opening should be understood to mean that at least the nose is inserted and includes insertion of only a part of the animal's head through the opening, as well as the entire head of the test animal. The thoracic chamber includes a test animal insertion opening opposite the seal, and a may include a pusher or plunger insertable through the insertion opening.
In use, the test animal is inserted into the chamber and, if necessary, pushed forward with the plunger so that the animal's head or a part thereof projects through the seal opening. The animal then breathes air within the nasal chamber, while it body is in the thoracic chamber. The thoracic expansion or changes in volume of the animal's body within the thoracic chamber due to inspiration and expiration can then be measured as the animal breathes. Simultaneously, as the animal breathes, air is drawn out of and pushed into the nasal chamber, and the nasal respiratory flow is measured by the nasal chamber. By measuring the two flows simultaneously, specific airway resistance can be derived, as well as other useful measures of pulmonary mechanics. Since specific airway resistance is a principal measure commonly sought using this technique, it is desirable to make a very good seal which does not introduce any resistance of its own.
Placement of a neck seal or nose seal onto a conscious animal while simultaneously restraining the animal within the test chamber can be very challenging to the operator. Therefore, there is a need for a plethysmograph designed to facilitate the insertion of the animal into the plethysmograph and proper seating of the seal around the animal's head.